Activation of an Aquareovirus, Chum Salmon Reovirus (CSV), by the CiliatesTetrahymena thermophilaandT. canadensis

Abstract

For the first time, ciliates have been found to activate rather than inactivate a virus, chum salmon reovirus (CSV). Activation was seen as an increase in viral titre upon incubation of CSV at 22 °C with Tetrahymena canadenesis and two strains of T. thermophila: wild type (B1975) and a temperature conditional mutant for phagocytosis (NP1). The titre increase was not likely due to replication because CSV had no visible effects on the ciliates and no vertebrate virus has ever been shown unequivocally to replicate in ciliates. When incubated with B1975 and NP1 at 30 °C, CSV was activated only by B1975. Therefore, activation required CSV internalization because at 30 °C only B1975 exhibited phagocytosis. CSV replicated in fish cells at 18 to 26 °C but not at 30 °C. Collectively, these observations point to CSV activation being distinct from replication. Activation is attributed to the CSV capsid being modified in the ciliate phagosomal-lysosomal system and released in a more infectious form. When allowed to swim in CSV-infected fish cell cultures, collected, washed, and transferred to uninfected cultures, T. canadensis caused a CSV infection. Overall the results suggest that ciliates could have roles in the environmental dissemination of some fish viral diseases.

Evaluation of zebrafish (Danio rerio) as an animal model for the viral infections of fish

“…Therefore, considering the advantages In vitro experiments revealed that in addition to SVCV, which is a well-described infection model in zebrafish, three other fish infecting viruses were able to replicate in ZF4 and SJD.1 cell lines: CSV, Winton et al, 1981). Very recently, CSV replication has also been reported in the zebrafish cell line ZEB2J (Pinheiro & Bols, 2018).…”

“…Several cell lines from different fish species, including salmonids, cyprinids, sunfishes, ictalurids and Percidae , have been already tested for CSV propagation, and the best virus replication was demonstrated in cells derived from salmonid fish (DeWitte‐Orr & Bols, ; Pinheiro & Bols, ; Winton et al, ). Very recently, CSV replication has also been reported in the zebrafish cell line ZEB2J (Pinheiro & Bols, ). In vitro CSV produces a cytopathic effect which is very characteristic, due to the presence of syncytia—large multinucleated giant cells resulting from the fusion of neighbouring cells (DeWitte‐Orr & Bols, ).…”

“…The virus was isolated in 1978 from a stock of adult Chum salmon (Oncorhynchus keta) being routinely tested to egg exportation in Japan (Winton et al, 1981). Several cell lines from different fish species, including salmonids, cyprinids, sunfishes, ictalurids and Percidae, have been already tested for CSV propagation, and the best virus replication was demonstrated in cells derived from salmonid fish (DeWitte-Orr & Bols, 2007;Pinheiro & Bols, 2018;Winton et al, 1981). Very recently, CSV replication has also been reported in the zebrafish cell line ZEB2J (Pinheiro & Bols, 2018).…”

Control of Waterborne Human Viruses by Indigenous Bacteria and Protists Is Influenced by Temperature, Virus Type, and Microbial Species

“…Similar findings were reported for single protist species, which were found to exert vastly different effects on different viruses. For example, studies on fish viruses and bacteriophages have shown that ciliates could inactivate viral hemorrhagic septicemia virus (29) and bacteriophage T4 (10), but they internalized and then released chum salmon reovirus and bacteriophage phiX174 in an infective state (30,31). Thus, our results suggest that, like for fish viruses or bacteriophages, not all human viruses are equally susceptible to protists.…”

Removal of Waterborne Viruses by Tetrahymena pyriformis Is Virus-Specific and Coincides with Changes in Protist Swimming Speed

“…Both virus and protist species determine whether or not a virus is susceptible to grazing, 4,6,15,16 and a single protist species (Tetrahymena spp.) can exert varying effects on different viruses, including activation, 17 protection, 18 or inactivation. 19 Virus susceptibility to grazing may be driven by a protist's ability to sense and uptake their prey, or by its capacity to digest it.…”